This invention relates to electromagnetic valve actuators for internal combustion engines or gas generators.
Existing proposals use counteracting spring pairs to power the valve from extreme positions. At static equilibrium the valve is half open. The disadvantage of spring power is that the rising force with displacement characteristic results in the need for powerful electromagnets using a 42V supply. A high current initiation pulse is also required to close the valve from the equilibrium position.
A second issue is the requirement to simultaneously seat the valve and armature when the assembly is naturally subjected to differential thermal expansion, manufacturing tolerances and seat wear. Moreover, the landing velocity must be controlled to less than 0.15 m/s to minimize contact noise.
The object of this invention is to solve the problems encountered with the existing proposals by providing a valve actuator which minimizes electrical power requirements so that engine valves can be controlled using existing low voltage vehicle systems.
According to the invention, there is provided a device for actuating a gas exchange valve of an internal combustion engine or gas generator, said device comprising an armature operatively connected to the valve stem of a valve member and at least one electromagnet arranged to act on the armature to move the valve member from the open to the closed position, wherein the armature is disposed in a chamber and wherein a gas pressure source is connected by a supply line to the chamber, the arrangement being such that reduction of the electromagnetic force on the valve member in the closing direction is effective to enable the gas pressure from said gas pressure source to move the valve member to the open position.
By utilizing gas pressure to open the valve, the power consumption of the electromagnets is greatly reduced because this is only used to close the valve. Return of the valve member to the closed position may be assisted by a return spring.
Elimination of the opening electromagnet also provides the opportunity to use fixed real time valve events to self supercharge the engine using standing pressure waves in fixed geometry exhaust and intake pipes independent of engine speed.
According to one embodiment of the invention, a second electromagnet is provided to assist in moving the valve member to the open position. In this embodiment, the valve opening and closing electromagnets are axially spaced and have opposing pole faces, the armature being disposed in the chamber between said pole faces.
The gas pressure provides an approximately constant force to open the valve, so that the electromagnet does not have to hold against the maximum force of a rising force system such as a coil spring. Further reductions in electromagnetic holding power are possible in systems without an opening electromagnet.
Preferably, a seal is provided between contact faces of the armature and closing electromagnet so that the area of the armature exposed to the gas pressure in the closed position of the valve is less than the total area of the armature. Such use of differential armature areas acted on by the gas pressure, dependent on its open or closed position, further reduces the electromagnetic holding power in proportion to the ratio of the areas.
The seal is preferably flexible in the axial direction and is arranged to be contacted by the armature in the closing direction of the valve member before the armature makes contact with the pole face of the closing electromagnet. Alternatively, the valve seat may be so disposed in relation to the pole face that the armature does not necessarily contact the pole face when the valve is closed.
A unidirectional seal is desirably provided between the armature and the chamber.
The return spring is desirably located in a compression chamber formed between the opening electromagnet and a stem of the valve member. A seal may be provided between the armature and the pole face of the opening electromagnet to reduce the armature area enclosing the compression chamber and thus the electromagnetic holding force required in the open position of the valve member.
The valve stem may be of tubular construction with exit ports in order that said valve stem can also function as a gas supply passage.